Re: Clinical factors associated with Merkel cell polyomavirus infection in Merkel cell carcinoma.

Sihto et al. ( 1 ) recently analyzed 114 formalinfixed and paraffin-embedded Merkel cell carcinoma (MCC) samples from a Finnish cohort for the presence of Merkel cell polyomavirus (MCPyV) DNA. They reported that the prevalence of MCPyV DNA in MCC was 79.8% and, surprisingly, that MCPyV DNA – positive MCCs were preferentially located on the limbs compared with MCPyV DNA – negative MCCs. Their data also suggested that patients with MCPyV DNA – positive tumors had a better prognosis and fewer regional nodal metastases at time of diagnosis compared with patients with MCPyV DNA – negative tumors. We asked if the fi ndings of Sihto et al. could be replicated in an independent cohort of MCC patients. We previously investigated 35 MCC tissue samples from 31 German patients for the presence of MCPyV DNA. We detected MCPyV DNA by polymerase chain reaction amplifi cation in 22 samples (63%) and in 21 patients (68%) ( 2 ) using two sets of primers. Polymerase chain reaction amplifi cation with these two primer sets resulted in a 138-base pair product (MCV138 forward: 5 ′ -GGTTAGAGAT GCTGGAAATGACC-3 ′ ; reverse: 5 ′ C A A A T A A G C A G C A G T A C C A GGC-3 ′ ) and a 191-base pair product (MCV191 forward: 5 ′ -CCACTTTATT ATCTTAGCCCAT-3 ′ ; reverse: 5 ′ -TCCT TTTGGCTAGAACAGTGTC-3 ′ ) that target the large and small T-antigen regions, respectively. The exact locations for the primer pairs are forward 2185 – 2207 and reverse 2301 – 2322 (MCV138) and forward 1994 – 2015 and reverse 2163 – 2184 (MCV191) and are based on reference sequences in the National Center for Biotechnology Information Entrez Nucleotide database (gb|EU375803.1, MCPyV isolate MCC350). All positive polymerase chain reaction results were confi rmed by Southern blot analysis as previously described ( 2 ). Of the 31 primary tumor tissue samples from the German MCC patients, 21 were positive for MCPyV DNA and 10 Table 1 . Clinicopathological data *